We propose a five-year Interdisciplinary Biology Initiative (IBI) at the Kavli Institute for Theoretical Physics (KITP) that will consist of a series of extended programs ranging thematically from Systems Biology, Bioinformatics and Genomics, to Neuroscience and Biophysics. We propose to hold 2 programs per year, each ranging from 4 to 12 weeks in duration. The long term goal of this initiative is to foster interactions between physical and mathematical scientists, computer scientists and engineers with life scientists, and to establish an interdisciplinary community focused on the development of new quantitative approaches to the study of important biological and biomedical problems. With its established role in the physics community, KITP is well positioned to recruit more physicists into interdisciplinary research. IBI is designed to function as a user facility for the interdisciplinary community with the programs proposed and organized by extramural teams of coordinators. The first two planned programs are: Dynamics of Development and Physics and Mathematics of Cancer. Subsequent programs are to be selected by the KITP Scientific Advisory Board in consultation with the external IBI Scientific Advisory Board. Selection will be based on four criteria: 1) relevance of the subject to life science; 2) potential impact of quantitative methods: 3) plans to assemble a diverse group of participants; 4) impact on education and training. The programs will be organized with the emphasis on germination of interdisciplinary collaborations and will include an extensive tutorial component to provide physical and mathematical scientists with the necessary biology background and to familiarize life-scientists with new quantitative approaches. Programs will achieve a balanced mixture of life-scientists with physical scientists and engineers and will involve scientists of all levels of seniority as well as a number of advanced graduate students. All program participants are encouraged to attend for an extended period with the minimum of 3 weeks being set for theorists. The proposed format of interdisciplinary biology programs has evolved in the past IBI programs at KITP and has proved to be successful both in fostering collaborations and in its educational impact. All programs are made publicly available via KITP website. In addition, we propose to sponsor educational outreach activities, including a workshop for high school science teachers.